Integrated barge tow with recessed bottom

ABSTRACT

An integrated barge tow for use on inland waterways having disconnectable bow and towboat sections and a plurality of interior box barges with recessed bottoms to capture an air bubble reducing resistance to movement through the water.

United States Patent McDermott et a1.

INTEGRATED BARGE TOW WITH RECESSED BOTTOM David C. McDermott; Errol V. Seymour, both of Houston, Tex.

Assignee: Shell Oil Company, New York, NY.

Filed: June 28, 1971 Appl. No; 157,211

Inventors:

U.S. C1. 114/235 R, 114/77 R Int. Cl B63b 21/00 Field of Search... 114/235 R, 77 R, 67 A, 236,

References Cited UNITED STATES PATENTS Gainsley 114/235 R Primary ExaminerDuane A. Reger Assistant ExaminerD. C. Butler [5 7] ABSTRACT An integrated barge tow for use on inland waterways having disconnectable bow and towboat sections and a plurality of interior box barges with recessed bottoms to capture an air bubble reducing resistance to movement through the Water.

7 Claims, 11 Drawing Figures PAINTED- 3.788.263

SHEEI 2 [IF 4 7 FIG. 5A

I D. C. McDermott i 2 5 1 l EV. Seymour 1" HWY INVENTORS PATENTH] JAN 2 9 IBM SHEET 3 0F 4 D. C. McDermott E V. Seymour 2 t t 2 5 8 4 I 1/ 6 b m L t T S M llriv 0 0 0 m W 5 0 5 INVE N TORS PAIENTED 3.788.263

saw u or 4 MST/{LOG 264.5+33.6t 141 l\ (D 300 Q \l 250 t(FT) FIG. 8

CONVENTIONAL BARGE WITHOUT AIR WATER //v CONTACT CUSHION y W/TH BOTTOM OF HULL 33 SKIRT DEPTH 7FT \l L &

ROLL ANGLE O RAD M E .V. Seymour INVENTORS FIG.9

1. INTEGRATED BARGE'TOW WITH RECESSED BOTTOM BACKGROUND OF THE INVENTION It is well known to those skilled in the art that in driving, pushing, or towing a vessel through the water a significant portion of the total resistance to movement relative to the water can be attributed to skin friction or drag. This skin friction can be extremely large in the case of .a flat bottom vessel such as a barge having shallow draft. Through the use of a thin layer of air between the barge hull and the water surface, the skin friction can be significantly reduced. Such a reduction in resistance to movement will enable a corresponding reduction in horsepower requirement of the tug moving the barge through the water.

Use of an air cushion is not new in such method utilized a continuous flow of compressed air circulating through several longitudinal channels extending along the underside of the hull, the compressed air entering the longitudinal channels in the .bow or forward section of the vessel and exiting at the rear or stern section of the vessel. This method required a large capacity air system as the channels are open at each end rather than closed to trap the air and prevent its escape. A barge of this design while being stable in roll would not provide sufficient stability to pitching motions since it does not incorporate any transverse skirts perpendicular to the longitudinal skirts on the underside of the hull. The numerous longitudinal channels also reduce the effective area of the air layer beneath the hull thereby decreasing the overall skin friction reduction.

Another method has utilizeda barge hull having a recessed bottom having numerous longitudinal extending channels, the channels being somewhat closed at the bow and stern ends to prevent escape of air supplied from compression facilities on the deck of the vessel. Roll stability of abarge of this design would be ensured due to the numerous longitudinalchannels on the underside of the hull, but at the same time these longitudinal channels reduce the surface of the air layer and add to the skin friction of the barge hull bottom. External forces such as waves that impart a pitching motion to a barge of this design would. impair the stability in pitch since the closures at the bow and stem ends are designed for use as air inlets to the recessed bottom and are not intended to be used as surfaces to maintain vessel stability in pitch. Sucha vessel would be subject to high air loss problems from the recessed hull defeating the purpose of using the air layer between the barge hull and water surface below. In a barge using the recessed hull design, the bow section design is important in order to minimize the standing waves produced by the bow as it moves through the water. Standing waves created by the bow section increase the skin friction of the barge hull following immediately behind the bow section as the standing waves would touch the recessed portion of the hull. The pitching problem in a barge of this design would arise between either the bow section does not provide adequate buoyancy or because the barge hull does not incorporate transverse members perpendicular to the longitudinal channels of the hull for compartmentation of the recessed hull.

Vessels having a recessed hull for minimizing skin friction are all of the design which have integral bow the art and one BRIEF DESCRIPTION OF THE INVENTION The invention relates tothe use of an integrated barge tow incorporating a captured air bubble (CAB) beneath the recessed hull of each interior box barge and is intended primarily for use on inland waterways and is not intended to be used as an ocean going barge tow. It has solved the problems of pitch and roll stability inherentin a barge having a recessed hull since instability in roll and pitch cause a vessel with a recessed hull to lose the captured air bubble diminishing any advantage that such a vessel might have over a conventional flat bottom barge. The barge of this invention uses thin longitudinal skirts on each side of the box barge, a center partitioning element along the keel, and transverse members at eachend and at the midpoint of each box barge such that the recessed hull is compartmented. The compartmentation restores roll and pitch stability to the box barge preventing excessive loss of air and preserving the captured air bubble.

The integrated barge tow when fully assembled will preferably have the bow unit and several interior box barges 'and the tug section, all being interconnected with rapid acting couplings of the railroad type such that the assembly may move forward in the water as a single integrated unit. It is so designed that it may quickly and conveniently be disconnected or separated into individual units for passing through narrow passages such as locks as are found along an inland waterway. After passage through locks as such it may quickly be reassembled for ease of travel up or down said waterway.

BRIEF DESCRIPTION OF THE DRAWING The advantage of the invention will be more fully und'erstood and appreciated with reference to the accompanying drawing in which:

FIG. 1 is a plan view of an integrated barge tow incorporating the captured air bubble concept;

FIG. 2 is a longitudinal sectional view of FIG. 1 on line 22 illustrating the configuration of the recessed hull design;

FIG. 3 is a transverse sectional view of FIG. 1 on the line 3-3 to show the compartmented design of the recessed hull;

FIG. 4 is a partial longitudinal sectional view on line 4-4 of FIG. 1 illustrating transverse skirts incorporated in the hull design of each individual barge.

FIG. 5 is a comparison of the righting moments of a conventional and non-compartmented CAB hull; FIG. 6 is a graphical representation of hull stability using a compartmented CAB hull and buoyant skirts;

FIG. 7 illustrates the stability moment versus skirt thickness for a non-compartmental CAB hull; and

FIG. 8 illustrates the stability moment versus skirt thickness for a compartmented CAB hull.

FIG. 9 illustrates the restoring in roll of a CAB hull with three longitudinal skirts.

A box-shaped barge with a non-compartmented air layer beneath it receives no restoring moment from pressure under the hull when given a pitch or roll impulse because the air beneath the hull retains a uniform pressure distribution whereas a conventional hull re ceives most of its stability from the change in pressure distribution beneath the hull when either a pitch or roll impulse is imparted to the barge. The difference is illustrated by FIG. 5.

It has been discovered that stability can be restored to a CAB hull by compartmentation more advantageously than by increasing the buoyancy of the skirts. Restoration of stability by use of wide buoyant skirts is undesirable for roll stability because they reduce the area of the'air layer and consequently minimize the magnitude of skin friction reduction. The two methods of stabilization are illustrated by FIG. 6. The following stability analysis in roll will show that by the use of three thin longitudinal skirts that approximately 75 percent of the hydrostatic restoring moment of a conventional box barge is maintained. 7

ACAB box barge with skirts of thickness is shown in FIG. 7. The static restoring moment of this barge, M can be written as MST=MW+MB+MS where M is the amount due to hydrostatic sidewall pressure MB is the nioment due to buoyancy force: on the skirt: M is the moment due to cushion pressure on the skirts The restoring moments are derived with the approximation of small displacements, i.e., second order efn is the number of transverse skirts of thickness t n 2 t is the thickness of the longitudinal skirts L, B 2b, H are the length, width and draft of the barge Substituting these moments into Equation (2) and letting L* E L and 1,, I 2 yields (3) The magnitude of the restoring moment is determined as a function of t by substituting some sample barge data: Preferably L 290 ft, H ft, g 2.6 ft, b 25 ft and n 2 into Equation (3). Then A plot of M 'yL b 0 versus t is shown in FIG. 7. This plot shows that the barge is subjected to a restoring moment only for t greater than about 1 foot. The negative restoring force for t 1 foot is due to the internal cushsubjected to hydrostatic forces increasing the restoring ion pressures on the skirts. It is also noted that large values of t are required to provide a sufficient restoring moment. For example, the restoring moment for a conventional barge of the same size without an air cushion would be M y L b 0(368.7). Obviously, the required increase in t reduces the drag reduction effect of the air cushion. To overcome this problem, another longitudinal skirt at the center of the hull is required.

As indicated in FIG. 8,'the addition of another longitudinal skirt changes the moments M and Mg and also introduces a restoring'moment M due to the differential in cushion 'pressuresion the hull. Again, neglecting second order effects, these moments can-be expressed (6) substitution of the numerical'values given previously, yields M T/y L b 0 264.5 33.6: 1.41

which is plotted in FIG-8. It is seen that the restoring moment now increases ata slower rate with increasing t. A comparison of FIGS. 7 and 8 shows that the addi' tion of a longitudinal skirt has greatly increased the magnitude of the restoring moment for small values of The restoring moment for a barge with three longitudinal'skirts and t E O is 72 percent of the hydrostatic restoring moment in a conventional box bargs. The increase in M ver'sus0 is shown in FIG. 9. As 0 becomes larger than 22 (0.04 rad), the roll angle at which air begins to escape from the cushion, part of the hull is moment as indicated in FIG. 9. The angle of 0.04 rad is for 1 foot skirt depth.

The stability analysis of a CAB barge in pitch for a box hull of the type utilized in integrated tows, is analogous to the above study of roll. By substituting B for L and l for b in the equations for roll, the corresponding equations in pitch are obtained. Employing the same reasoning as before, it can be seen that a CAB barge re quires three transverse skirts to provide sufficient stability. Therestoring moment for skits of almost zero thickness is then (where L 21):

- where 4) is the pitch angle. Substituting numerical values into this equation it is found that the restoring moment in pitch of a CAB barge is 75 percent of the hydrostatic moment of a conventional barge. The restoring moments due to sidewall pressure and cushion pressure on the skirts are negligible in pitch which accounts for the slight increase in the fractional moment in pitch (75 percent) as compared to roll (72 percent).

DESCRIPTION OF A PREFERRED EMBODIMENT Use of an integrated tow is not new in the art but the use of a captured air bubble in an integrated tow is new in the art. The invention contemplates the use of a Separate bow and towboat sections, the bow section incorporating either a three dimension raked bow for higher speeds or two dimensional rake bow for slower speeds. The bow and towboat sections will also be capable of being suitably joined if there are no interior box barges in the tow. The bow section also incorporates guidance means preferably above the hull such as a bow thruster of the water jet type so that when operating in shallow water it will not be damaged. The towboat section is provided with propelling means and is equipped with suitable air compression or supply means to furnish air for the interior box barges. All interior box barges are of identical design so that the integrated tow moves up or down stream' to various docking facilities along the route, individual box barges may either be picked up as 'part of the tow or docked at appropriate facilities.

Through the use of the captured air bubble, horsepower requirements of the tug can be reduced by as much as 40 percent when'compared to a conventional box barge transporting equivalent cargo.

The bow unit and the towboat are designed so that the overall shape of the-integrated tow is optimum for the operating conditions, and so that they form a hydrodynamically smooth vessel when combined with the interior box barges. For instance, the bow unit might be ship-shaped for high speed operations, or might have a traditional barge shape for low speed operations, while the towboat shape would be such as to minimize drag and provide optimum waterflow to the propeller. The towboat and bow unit are designed to be free of cargo, so that part of the equipment presently carried on the towboat can be placed in the bow unit, as for example fuel.

Referring to the drawings andv more particularly to FIG. 1 in which an integrated barge tow with the bow section 1, towboat section or tug 2, and three intermediate box barges 15, all being coupled together by a connecting means to form an integrated barge tow resting in water 7. There can be one, to several box barges connected together between bow section 1 and tug section 2. Connecting means 10 is a rapid acting coupling such that all box barges 15 may move vertically in response to wave action independently of each other and are of the railroad type having a fixed half in combination with a movable half. Bow section 1 may be of the high speed design of shipshaped as shown by the drawing or it may be of theslow speedconventional spoon bow design and incorporate bow thrusters 6 for guidance or maneuverability. The towboat section is of conventional design except that in this case it has incorporated into its design a suitable compressor 12 in order that it may supply compressed air to the box barges recessed hull 8 through integral conduits 14 to the air supply ports 13. Each box barge, if so desired, may incorporate individual air regulators 16 in the integral air conduits 14 so that air distribution to each box barge may be individually controlled if desired depending upon barge cargo. I

Referring now to FIG. 3, the recessed hull 8 of box barge 15 is formed by identical longitudinal skirts 3 and 4 on each side of center partitioning element 5, and transverse skirt 11 at each end. Longitudinal skirts 3 and 4 are formed by extending longitudinal side wall 17 below the plane of recessed hull 8. Longitudinal skirts 3 and 4 are thin, usually in the range of 3 inches to 12 inches. The inside of longitudinal skirts 3 and 4 extend upwardly and inwardly to-form a smooth surface where they join recessed hull 8. The depth that longitudinal skirts 3 and 4 extends below the recessed hull 8 is important in view of air leakage and roll stability. This depth is usually in the range of 1 foot to 2 feet. Center partitioning element 5 extends longitudinally along the,

keel section of the barge hull and divides recessed hull 8 into equal halves. The width of center partitioning element 5 is approximately the same as longitudinal skirts 3 and 4. Center partitioning element 5 forms a smooth surface with recessed hull 8 where it 1 joins the hull. Center partitioning element 5 is particularly important to the barge for roll stability as it prevents uniform pressure distribution under the recessed hull 8 when given a roll impulse from waves or other external forces to the barge l5. Unequal pressure distribution is important in order that the restoring moment is of sufficient magnitude to maintain stability. Transverse skirt 11 is formed by extending end plate 9 below the plane of recessed hull 8 to a depth below recessed hull equal to longitudinal skirts 3 and 4, and center partitioning element 5. Transverse skirt 11 extends the full width of box barge 15 and forms a smooth transition at its joinder'with recessed hull 8. If the transverseskirts 11 are thin then it is usually preferable to add a third transverse skirt 11 at the midpoint of box barge 15. This is done to provide sufficient pitch stability for box barge 15. t

We claim as our invention: 1. An integrated barge tow for use on inland waterways comprising;

a disconnectable bow section; a disconnectable towboat section; at least one interior box barge having a recessed bottomcomprising a hull section, a thin longitudinal skirt extending below the plane of the hull on each side of the barge, a longitudinal center partitioning element extending below'the plane of the hull the same distance as the longitudinal skirts and a plu rality of thin transverse skirts extending below the plane of the hull the same distance as the longitudinal skirts and longitudinal center partitioning element, said transverse skirts being perpendicular to both the longitudinal skirts and longitudinal center partitioning element and intersecting both said longitudinal skirts and longitudinal center partitioning element to form a compartmented recessed bottom; and

connecting means joining said bow Section, towboat section, and box barge to form a single unit, wherein said connecting means includes first connecting means for operatively connecting said bow section to said box barge, second connecting means for operatively connecting said towboat section to said box barge,'and third connecting means for operatively connecting said box section to said towboat section when said box barge is removed.

3,788,263 7 8 2. The tow of claim 1 wherein said towboat section porates bow thrusters for improved maneuverability.

has a Compressed air pp y- 6. The tow of claim 1 wherein said plurality of box 3. The tow of claim 1 wherein said recessed bottom barges are identical is for capturing an air bubble. v

4. The tow of claim 1 wherein said connecting means 5 tow of clalm l wherem the plurality of transis of the rapid-acting coupling type. Verse skms total 5. The tow of claim 1 wherein said bow section incor- 

1. An integrated barge tow for use on inland waterways comprising; a disconnectable bow section; a disconnectable towboat section; at least one interior box barge having a recessed bottom comprising a hull section, a thin longitudinal skirt extending below the plane of the hull on each side of the barge, a longitudinal center partitioning element extending below the plane of the hull the same distance as the longitudinal skirts and a plurality of thin transverse skirts extending below the plane of the hull the same distance as the longitudinal skirts and longitudinal center partitioning elemenT, said transverse skirts being perpendicular to both the longitudinal skirts and longitudinal center partitioning element and intersecting both said longitudinal skirts and longitudinal center partitioning element to form a compartmented recessed bottom; and connecting means joining said bow section, towboat section, and box barge to form a single unit, wherein said connecting means includes first connecting means for operatively connecting said bow section to said box barge, second connecting means for operatively connecting said towboat section to said box barge, and third connecting means for operatively connecting said box section to said towboat section when said box barge is removed.
 2. The tow of claim 1 wherein said towboat section has a compressed air supply.
 3. The tow of claim 1 wherein said recessed bottom is for capturing an air bubble.
 4. The tow of claim 1 wherein said connecting means is of the rapid-acting coupling type.
 5. The tow of claim 1 wherein said bow section incorporates bow thrusters for improved maneuverability.
 6. The tow of claim 1 wherein said plurality of box barges are identical.
 7. The tow of claim 1 wherein the plurality of transverse skirts total
 3. 